The b'->tW Analysis Working Page

Introduction: Physics and Signatures

The Standard Model (SM) with three generation of quarks has successfully explained most of the physics phenomena up to date. The fourth generation searches cooled off since the limit on the neutrino flavors, and the precise measurement on the electroweak parameters seems to be against the possibility of an extra fermion family. However, it does not guarantee the nonexistence of fourth generation of quarks. The SM is not yet a complete theory, and the options for new physics phenomena are still open.

High energy frontier experiments, such as CDF and D0 at the Tevatron, have performed searches for the fourth generation quarks. CDF has announced their result for seaching a b' quark decaying to tW final state. The study consists of searching for same-sign dilepton pairs based on a data sample of 2.7 fb^-1. The observed events in data (two events) are consistent with the background expectation of 1.9 events. The best limit on the b' mass is 325 GeV/c^2 at 95\% confidence level.

According to different assumptions of the relative strength of |Vcb'| and |Vtb'|, both b' -> cW and b' -> tW(*) could be the major b' decays if m(b') is less than m(t) + m(W) ~ 255 GeV/c^2. For the case of m(b') > 255 GeV/c^2, the decay b' -> tW is open and expected to be the dominant channel. The transition b' -> cW would be suppressed for such a heavy b' scenario unless with a large Vcb'. The decay b'-> t' should be kinematically suppressed [if m(t) < m(t') < m(b')], and b' -> b modes are only proceed through the second order loop diagrams.

When both b' quarks decay into top quark and W boson, it becomes a four W final state. The basic signature is bbWWWW for the pp -> b'b' production. Each W boson can decay through either leptonic W -> l nu or hadronic W -> di-jet. We order the possible final states according to the number of leptonic W's as follows:

• Mono-leptonic b'b' -> Wlnu Wjj Wjj Wjj + bb:

If we consider that the W bosons from b' decays decay hadronically, such events are practically tt + 4 jets events. Since there is only one neutrino in the final state, one can fully reconstruct the events with the missing energy measurement.

• Dileptonic b'b' -> Wlnu Wlnu Wjj Wjj + bb:

We categorize the dileptonic channels into two signatures, one with opposite-sign leptons and the other one with same-sign leptons in the final state. The former one contains three topologies: prompt W -> l nu decays (fully hadronic ttbar), dileptonic ttbar, or a fully dileptonic b' decays (while the other b' decays fully hadronically). Only the last topology has a b' quark that can be fully reconstructed for the mass measurement. The signature of same-sign leptons is unique and the backgrounds from the Standard Model are negligibly small. It is only produced through a leptonic top and a leptonic W, but they are not decaying from the same b' quark. Thus, the b' quark cannot be fully reconstructed for same-sign dileptonic events.

• Trileptonic and quadrileptonic b'b' -> Wlnu Wlnu Wlnu Wjj + bb and b'b' -> Wlnu Wlnu Wlnu Wlnu + bb:

The sub-branching ratios for the trileptonic mode and the quadleptonic mode are much smaller comparing to the former two categories. Both modes have very unique decay signatures and free from most of the SM backgrounds. The b' quark cannot be reconstructed for all of these modes.

This effort is running under the Exotica physics group: https://twiki.cern.ch/twiki/bin/view/CMS/EXOTICA

Related Participants

Institution	Related People	Remark
National Taiwan University	Kai-Feng (Jack) Chen*, Rong-Syang Lu, Yen-Ming Tzeng, Jui-Te Wei, Yeong-Jyi Lei, Kai-Yi Kao, Yu-Wei Chang, Paolo Bartalini, Wei-Shu (George) Hou	*Contact person
Rutgers University	Steve Schnetzer, Dmitry Hits

• Cooperating with the Top partner analysis, https://twiki.cern.ch/twiki/bin/view/CMS/ExoticaTopPartners, contact person: Tulika Bose

Document & Presentations

• Physics references
  • Flavor changing neutral currents involving heavy quarks with four generations. A. Arhrib and W.-S. Hou. JHEP07(2006)009
  • Quarks and leptons beyond the third generation Phys. Rep. 330 263(2000). P.H. Frampton, P.Q. Hung and M. Sher.

10 TeV analysis (EXO-09-012):

General remark: A "minimum" update to the previous 14 TeV analysis (EXO-08-009). Since the 300 GeV/c^2 b'->rW has been already excluded by CDF and the initial energy of LHC will not reach 14 TeV, thus this analysis is carried out with the following two updates:

• Instead of 100/pb integrated luminosity at 14 TeV, this update study targets an initial data set of 200/pb at 10 TeV cm energy.
• The default reference signal is 400 GeV/c^2 b'->tW (instead of 300 GeV as in the previous analysis).

• Analysis note: CMS AN-2008/090
• PAS: PAS EXO-09-012

• Link to the presentations:
  • Pre-approval - 2 June 2009
  • CMS Exotica - 19 May 2009

14 TeV analysis (EXO-08-009):

Analysis Codes

• "bprimKit": See ExoticaPat for details.

The PAT embedded analysis code, now it's working with CMSSW_2_2_X (X<=9 as PAT version 1). Current version running under 2_2_9 together with the PAT patches (See SWGuidePATRecipes for 2_2_X PAT version 1). The current working code can be found at /afs/cern.ch/user/k/kfjack/public/bprimeKit with a single source code, build file, and a testing configuration file.

• "BprimeAnalyzer" by R.-S. Lu:

The analysis code works for CMSSW_1_6_X series. It produce a general format root tree for b'b -> multi-W analysis.

• "Heavybprime" (this is obsolute.):

The original analysis code for CMSSW_1_3_X series analysis. It produce simple raw-wise ntuples for the further studies. The code can be found at /afs/cern.ch/user/k/kfjack/public/Heavybprime.

Monte Carlo Samples

10 TeV Samples (2_1_X and 2_2_X)

Process	Cross-section (pb)	Size	Equ. Lumi (pb^-1)	Generator	Simulator	Remark
bprime, M(b') = 300 GeV/c^2	13.6(LO)	53.4K	3,930	Pythia	Full
bprime, M(b') = 400 GeV/c^2	2.80(LO)	40.8K	14,600	Pythia	Full
bprime, M(b') = 500 GeV/c^2	0.78(LO)	40.8K	52,300	Pythia	Full
tt+jets	414(NLO)	1.03M	2,490	Madgraph	Full
tt+W(+j)	0.33(LO)	8K	24,200	Madgraph	Full
tt+Z(+j)	0.32(LO)	8K	25,000	Madgraph	Full
ttW^+W^-	0.0035(LO)	4K	1,140,000	Madgraph	Full
W+jets	40,000(LO)	10.3M	258	Madgraph	Full
Z+jets	3,700(LO)	1.2M	324	Madgraph	Full
W+jets	40,000(LO)	101.3M	2530	Madgraph	Fast
Z+jets	3,700(LO)	9.7M	2630	Madgraph	Fast
WW inclusive	74.0(LO)	204K	2,760	Pythia	Full
ZZ inclusive	10.5(LO)	201K	19,100	Pythia	Full
WZ inclusive	32.0(LO)	249K	7,780	Pythia	Full
same-sign WW+jj	0.28(LO)	6K	21,400	Madgraph	Full
QCD (5 flavors, HT: 100-250 GeV)	15,000,000(LO)	14.2M	0.95	Madgraph	Full
QCD (5 flavors, HT: 250-500 GeV)	400,000(LO)	5.4M	13.5	Madgraph	Full
QCD (5 flavors, HT: 500-1000 GeV)	14,000(LO)	4.9M	350	Madgraph	Full
QCD (5 flavors, HT: 1000-inf GeV)	370(LO)	1.0M	2,700	Madgraph	Full

14 TeV Samples (1_8_4)

• Other stuff:
  • Configuration files for CSA07 production can be found at: /afs/cern.ch/user/k/kfjack/public/CSA07SUSYBSM_bprimetWtW

Tasks and Issues

Topic	Short comment	People
Trigger	which trigger streams that we want to use (for the early discovery)
Muon	Muon selectons and isolation
Electron	Electron selectons and isolation
Charge mis-ID rate	how to measure this number from data
Jets	Jet selecton (algorithms, threshold)
	Jet counting (how to examine this from data)
	Effects of pile-ups
Event selecton	What are the variables to be used, thresholds
	How to estimate the background level from data
Cross-section extraction	Adopting the counting experiment
	Systematic uncertainties
	Significance calculations

Useful Links

• Reference for systematic studies
  • Electron (Robust ID, Isolation, Trigger): Electroweak electron analysis note AN-2007/026
  • Muon (Isolation, Trigger): Electroweak muon analysis note AN-2007/031
  • Muon ID: CMS AN 2008/098
  • Measurement of jet energy scale corrections using top quark events: CMS PAS TOP-07-004
  • Top quark cross sections @ 100/pb: CMS PAS TOP-08-002

-- KaiFengChen - 14 Jun 2008